Snake-Inspired Kirigami Skin for Lateral Undulation of a Soft Snake Robot

Frictional anisotropy, as produced by the directionality of scales in snake skin, is necessary to propel snakes across flat, hard surfaces. This work illustrates the design, fabrication, and testing of a snake-inspired skin based on kirigami techniques that, when attached to a soft snake robot, improves the robot's locomotion capabilities when implementing a lateral undulation gait. Examination of snake scales in nature informed the shape and texture of the synthetic scales, which are activated through the buckling of kirigami lattices. Biological snakes have microornamentation on their scales, which is replicated by scoring ridges into the plastic skin. This microornamentation contributes to the lateral resistance necessary for lateral undulation. The skin's frictional properties were experimentally determined, as were their contributions to the locomotion of the robot across a flat, hard, textured surface. Contributions to locomotion from scale profile geometry, scale microornamentation, and scale angle of attack were identified. The range of longitudinal COF ratios was 1.0 to 3.0 and the range of lateral COF ratios was 0.9 to 3.3. The highest performing skin was the triangular scale profile with microornamentation, producing a velocity of 6 mm/s (0.03 BL/s) which is an increase of 335% over the robot with no skin when activated to maximum achievable curvature.